Hi. I've had my Canon 50mm f1.4 for a few months now and I'm wondering why when I turn the focus ring to either extreme it doesn't stop, it keeps moving with a kind of mushy tension. I'm not sure how far it goes as I'm afraid to test it. Yes I have the lens in MF mode.

Just so you're not relying on a single answer - as Severian the Lame said this is a normal characteristic of Canon's full-time manual focus lenses. You can rotate the ring as far as you like and you won't cause any damage.

All but one of the full-time manual lenses use the "Ring USM" focusing mechanism which cleverly employs a differential to allow the AF motor and the focusing ring to operate at the same time. There is one exception which uses the inferior "micro USM" motor together with a separate clutch to simulate the behaviour of Ring USM - and guess what, it's the 50/1.4. It seems to work fine but based on reports on this forum the failure rate seems to be higher than for other mechanisms.